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This article mainly explains "how to generate random integers by Java". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn how to generate random integers by Java.

1. Java.util.Random

This Random (). NextInt (int bound) generates a random integer from 0 (inclusive) to bound (excluding).

(1) Code snippet

For getRandomNumberInRange (5,10), this produces a random integer between 5 (inclusive) and 10 (inclusive).

Private static int getRandomNumberInRange (int min, int max) {if (min > = max) {throw new IllegalArgumentException ("max must be greater than min");} Random r = new Random (); return r.nextInt ((max-min) + 1) + min;}

(2) what is (max-min) + 1) + min?

The above formula produces a random integer between min (inclusive) and max (inclusive).

/ / Random () .nextInt (int bound) = Random integer from 0 (inclusive) to bound (exclusive) / / 1.nextInt (range) = nextInt (max-min) new Random () .nextInt (5); / / [0.4] [min = 0, max = 4] new Random (). NextInt (6); / / [0.5] new Random (). NextInt (7) / / [0.6] new Random () .nextInt (8); / / [0.7] new Random () .nextInt (9); / / [0.8] new Random () .nextInt (10); / / [0.9] new Random () .nextInt (11) / / [0.10] / / 2. To include the last value (max value) = (range + 1) new Random () .nextInt (5 + 1) / / [0.5] [min = 0 Max = 5] new Random (). NextInt (6 + 1) / / [0.6] new Random (). NextInt (7 + 1) / / [0.7] new Random (). NextInt (8 + 1) / / [0.8] new Random (). NextInt (9 + 1) / / [0.9] new Random (). NextInt (10) + 1) / / [0.10] new Random () .nextInt (11 + 1) / / [0.11] / / 3. To define a start value (min value) in a range / / For example The range should start from 10 = (range + 1) + min new Random (). NextInt (5 + 1) + 10 / / [0.5] + 10 = [10.15] new Random () .nextInt (6 + 1) + 10 / / [0.6] + 10 = [10.16] new Random () .nextInt (7 + 1) + 10 / / [0.7] + 10 = [10.17] new Random (). NextInt (8 + 1) + 10 / / [0.8] + 10 = [10.18] new Random (). NextInt (9 + 1) + 10 / / [0.9] + 10 = [10.19] new Random () .nextInt (10 + 1) + 10 / / [0.10] + 10 = [10 .. 20] new Random (). NextInt (11 + 1) + 10 / / [0.11] + 10 = [10.. 21] / / Range = (max-min) / / So The final formula is ((max-min) + 1) + min / / 4. Test [10.. 30] / / min = 10, max = 30 Range = (max-min) new Random (). NextInt ((max-min) + 1) + min new Random (). NextInt ((30-10) + 1) + 10 new Random (). NextInt ((20) + 1) + 10 new Random (). NextInt (21) + 10 / / [0.20] + 10 = [10. 30] / 5. Test [15. 99] / / min = 15 Max = 99, range = (max-min) new Random (). NextInt ((max-min) + 1) + min new Random (). NextInt ((99-15) + 1) + 15 new Random (). NextInt ((84) + 1) + 15 new Random (). NextInt (85) + 15 / / [0.84] + 15 = [15.99] / / Done, understand?

(3) generate a complete example of 10 random integers ranging from 5 (inclusive) to 10 (inclusive).

Package com.mkyong.example.test;import java.util.Random;public class TestRandom {public static void main (String [] args) {for (int I = 0; I)

< 10; i++) { System.out.println(getRandomNumberInRange(5, 10)); } } private static int getRandomNumberInRange(int min, int max) { if (min >

= max) {throw new IllegalArgumentException ("max must be greater than min");} Random r = new Random (); return r.nextInt ((max-min) + 1) + min;}}

Output

seven

six

ten

eight

nine

five

seven

ten

eight

five

two。 Mathematics。 Random

This Math.random () gives a random double value from 0. 0 (inclusive) to 1. 0 (excluding).

(1) Code fragment. Reference 1.2 is more or less the same formula.

(int) (Math.random () * ((max-min) + 1)) + min

(2) generate a complete example of 10 random integers in the range 16 (inclusive) to 20 (inclusive).

Package com.mkyong.example.test;public class TestRandom {public static void main (String [] args) {for (int I = 0; I)

< 10; i++) { System.out.println(getRandomNumberInRange(16, 20)); } } private static int getRandomNumberInRange(int min, int max) { if (min >

= max) {throw new IllegalArgumentException ("max must be greater than min");} return (int) (Math.random () * (max-min) + 1) + min;}}

Output

seventeen

sixteen

twenty

nineteen

twenty

twenty

twenty

seventeen

twenty

sixteen

3. Java 8 Random.ints

In Java 8, a new method java.util.Random has been added

Public IntStream ints (int randomNumberOrigin, int randomNumberBound) public IntStream ints (long streamSize, int randomNumberOrigin, int randomNumberBound)

This Random.ints (int origin, int bound) or Random.ints (int min, int max) generates a random integer from the origin (inclusive) to the binding (excluding).

(1) Code fragment.

Private static int getRandomNumberInRange (int min, int max) {Random r = new Random (); return r.ints (min, (max + 1)) .findFirst () .getAsInt ();}

(2) generate a complete example of 10 random integers in the range 33 (inclusive) to 38 (inclusive).

Package com.mkyong.form.test;import java.util.Random;public class TestRandom {public static void main (String [] args) {for (int I = 0; I < 10; iTunes +) {System.out.println (getRandomNumberInRange (33,38)) }} private static int getRandomNumberInRange (int min, int max) {Random r = new Random (); return r.ints (min, (max + 1)) .limit (1) .findFirst () .getAsInt ();}}

Output

thirty-four

thirty-five

thirty-seven

thirty-three

thirty-eight

thirty-seven

thirty-four

thirty-five

thirty-six

thirty-seven

(3) extra for your own reference.

Generates a random integer in the range of 33 (inclusive) and 38 (excluding) with a stream size of 10. And print out with forEach.

/ / Java 8 only new Random () .ints (10, 33, 38) .forEach (System.out::println)

Output

thirty-four

thirty-seven

thirty-seven

thirty-four

thirty-four

thirty-five

thirty-six

thirty-three

thirty-seven

thirty-four

At this point, I believe you have a deeper understanding of "how to generate random integers by Java". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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